Proceedings Paper

The NASA Living With a Star (LWS) Sentinels mission is presently being defined by its Science and Technology Definition Team (STDT). Sentinels is the third element of the LWS program. Its primary scientific objective is to discover, understand and model the connection between solar phenomena and the interplanetary/geospace disturbances, specifically, the heliospheric initiation, propagation and solar connection of those energetic phenomena that adversely affect space exploration and life and society here on Earth. Sentinels will play a particularly important role in support of NASA's new Vision for Space Exploration (VSE), in providing key new measurements required to understand the production of Solar Energetic Particles (SEPs) that are hazardous to human and robotic missions to the Moon and Mars. Here we describe the planning for Sentinels, and the preliminary design of the first phase, the Inner Heliosphere Sentinels, a four spacecraft mission to provide multi-point longitudinally and radially distributed in situ observations of SEPs, plasma, fields, and X-rays/gamma-rays/neutrons in the inner heliosphere (~0.25-0.76 AU), close to the site of SEP acceleration and rapid transient evolution.